1. Field of the Invention
The present invention relates to a process for closing a piston-cylinder unit, in particular a shock absorber. Such a piston-cylinder unit generally includes a cylinder tube in which there is an axially movable piston rod, whereby the piston rod is guided by means of a piston rod guide having a seal which closes the cylinder tube. A closing tool can preferably be used to bead an edge of the cylinder tube, which edge projects beyond the piston rod guide so that the bead can hold the piston rod guide in the cylinder tube.
2. Background Information
German Patent Application No. 41 12 956 discloses a process for closing a shock absorber in which the edge of the cylinder tube wall is beaded and rolled flat by means of rotating and pivoting rollers. The limits of this application are reached precisely with small cylinder tube diameters and rather large wall thicknesses, since the axial forces necessary for rolling are typically on a very high level.
Federal Republic of Germany Utility Model NO. G 83 11 750 discloses a shock absorber in which the cylinder tube exhibits reductions of its cross-section which make possible a partial beading of the edges of the cylinder tube by means of radially adjustable closing tools or dies. The reduction in the cross section entails a significant reduction in the force which can be applied, which essentially can only be compensated by means of an even greater wall thickness, so that the actual cylinder tube is over-sized. Tests performed on cylinder tubes without reductions in the cross-section revealed unacceptable cracks at the transition points from the partial beading of the edges to the adjacent wall sections of the cylinder tube.